Mac mini randomly reboots while idle or asleep

Your SHUTDOWN_TIME and BOOT_TIME entries show that the previous session ended at 21:29:58 and the next boot began at 21:30:17, but they do not establish whether macOS performed a normal shutdown, experienced an unexpected restart, or encountered a problem during sleep/wake.

First, check for scheduled power events:

pmset -g sched

Apple documents this command for displaying scheduled startup, sleep, wake, restart, and shutdown events. (Apple Support)

Then check the current power-management configuration:

pmset -g

and look for a recorded shutdown cause:

log show --last 24h --predicate 'eventMessage CONTAINS[c] "shutdown cause"' --info

Also check for diagnostic reports created around the time of a restart:

ls -lt /Library/Logs/DiagnosticReports/ | head -30

If a report containing panic, Kernel, or Sleep Wake corresponds to the restart time, its contents may provide useful evidence.

Because the Mac is a desktop Mac and the problem occurs while idle/asleep, if the logs does not  identify the cause, temporarily disconnecting all peripherals except the display, keyboard, and mouse/trackpad is a useful next test. 

Apple specifically recommends this when investigating unexpected restarts and suggests reconnecting devices individually if the problem stops. (Apple Support)

I would leave the power-management settings unchanged for now. The results from these checks should be collected before making configuration changes.

Apple: If your Mac restarted because of a problem

Apple: Schedule your Mac to turn on or off in Terminal

The three command outputs and any diagnostic report corresponding to one of the restart times are the most useful information to examine next.

Your results do not yet establish why the Mac is rebooting. They also do not, by themselves, establish that the reboot was caused by a kernel panic.

The SHUTDOWN_TIME and BOOT_TIME entries confirm that the Mac shut down and subsequently booted, but they do not identify the cause.

The most useful item to examine next is the diagnostic report created at 21:30:06, approximately 10 seconds after the reported reboot at 21:29:56:

shutdown_stall_2026-09-07-213006_koborns-MacBook-Pro-2.shutdownStall

Its timing is noteworthy, but the filename alone does not establish what caused the reboot.

pmset -g sched also shows a scheduled wake at 21:30:30 by com.apple.acmd.alarm. 

This confirms that a system wake event was scheduled around the same time, but the information available does not establish that it was related to the reboot. 

Apple documents pmset -g sched as the command for displaying scheduled power events. (Apple Support)

The pmset -g output shows that sleep was being prevented by powerd and bluetoothd when you ran the command. This is relevant to the sleep investigation, but it does not identify either process as the cause.

The log show command returned no shutdown-cause information, so it has not provided a cause.

At this stage, I would not change the scheduled power settings or perform more invasive troubleshooting. 

The next step is to examine the shutdownStall diagnostic and, if necessary, then determine whether the evidence points toward a software problem, connected peripheral, power-management issue, or hardware problem.

If the diagnostic evidence does not identify the cause and the unexpected restarts continue,

Apple recommends progressively isolating software and hardware, including Safe Mode, disconnecting peripherals, and Apple Diagnostics. (Apple Support)

Look through it specifically for:

• the process or processes involved in the shutdown stall;
• threads blocked on locks, I/O, or power-management operations;
• repeated or unusually long stack traces;
• references to powerd, kernel, bluetoothd, APFS, disks, USB/Thunderbolt devices, or third-party software;
• timestamps and state transitions that might help distinguish an orderly shutdown, a stalled shutdown, or an unexpected restart.